1. Field of the Invention
This invention relates to a sheet conveying apparatus used for a photocopier, printer, facsimile machine, or hybrid machine which is a combination of the aforementioned machines and to an image forming apparatus having the sheet conveying apparatus.
2. Description of Prior Art
An electrophotographic photocopier as an example of conventional image forming apparatuses is structured to correct oblique feeding of sheets by striking a nipping portion of a register roller, the sheets fed from a sheet supplying section to an image forming section while the register roller arranged right before the photosensitive drum of the image forming section is stopped.
In a photocopier having a long conveyance route from the sheet supplying section to the image forming section, a subsequent sheet is fed one by one without awaiting image formation on a proceeding sheet at the photosensitive drum in order to render higher the productivity of the photocopier. Plural sheets therefore exist in the conveyance route from the sheet supplying section to the image forming section.
Because the sheet is substantially stopped at a position of the register roller at a timing correcting oblique feeding of the sheets, the subsequent sheets are temporarily stopped at a sheet interval in accordance with that stoppage so that the subsequent sheets do not catch up to this sheet. Then, the plural sheets in the conveyance route are controlled to resume being fed by driving at the same time the register roller located right before the photosensitive drum and the rollers located from the sheet supplying section to the photosensitive drum in association with the timing of image rotation on the photosensitive drum. The register roller feeds the sheet to the photosensitive drum, and the register roller is stopped after the rear end of the sheet passes the register roller to prepare for arrival of the subsequent sheet.
As one means for conveying sheets with remarkably short sheet intervals in the conveyance route from the sheet supplying section to the register roller, and as disclosed in Japanese Pre-Granted Publication (A1) No. 2000-211,756, there is an apparatus that feeds sheets such that the rear end of the proceeding sheet and the front end of the subsequent sheet are partly overlapped when the sheets are fed subsequently from the feeding cassette to the image forming section.
It is desirable to improve further the productivity of such a conventional photocopier, and to do so, it is necessary to increase the conveyance speed or to reduce the sheet interval. Even using the apparatus shown in Japanese Pre-Granted Publication (A1) No. 2000-211,756 in which the sheets are fed upon overlapping the sheets from the feeding cassette, the sheet overlapped feeding cannot satisfy the demand because feeding is made alternatively from the cassette feeding and the double side feeding when images are formed on the double sides.
Higher productivity when duplex printing is becoming expected as the apparatus feeding sheets faster, and very sensitive timing is required to merge the sheets in keeping the sheet interval constant at the junction of the sheets from the double side section and the cassette.
This invention is for a sheet conveying apparatus comprising: a first conveying means for conveying a sheet; a second conveying means for conveying a sheet in merging with the first conveying means; and a sheet merging overlapping means for overlapping, at a junction between the first and second conveying means, the sheet conveyed by the first conveying means with the sheet conveyed by the second conveying means in a sheet conveyance direction.
This invention is also for a sheet conveying apparatus comprising: a first conveyance route for guiding a sheet conveyed by a first conveyance roller for conveying the sheet; a second conveyance route for guiding a sheet conveyed by a second conveyance roller for conveying the sheet; and a controller for controlling the drive and stop of the first and second conveyance rollers, wherein the first conveyance route and the second conveyance route are merged, and wherein the controller so controls the drive and stop of the first and second conveyance rollers as to convey the sheets in overlapping, at a junction between the first and second conveyance routes, the proceeding sheet guided by one of the first and second conveyance routes with the subsequent sheet guided by the other in a sheet conveyance direction.
This invention is further for a sheet conveying apparatus comprising: a first conveyance route for guiding a sheet conveyed by a first conveyance roller; and a second conveyance route for guiding a sheet conveyed by a second conveyance roller in merging the first conveyance route, and having an overlapping conveyance mode for conveying the sheets in overlapping the proceeding sheet guided by one of the first and second conveyance routes with the subsequent sheet guided by the other in a sheet conveyance direction, and an overlapping canceling mode for canceling the conveyance overlapping the proceeding sheet with the subsequent sheet and separating the proceeding sheet from the subsequent sheet.